Science Content Specific Vocabulary

Terminology specific to Chemistry, Biology, Physics, and Earth & Space Sciences

Matter

Anything that has mass and takes up space.

Solid

Matter that keeps its own shape and volume.

Liquid

Matter with a set volume that takes the shape of its container.

Gas

Matter with no set shape or volume. Its particles move fast and spread out.

Melting

Changing from a solid to a liquid.

Freezing

Changing from a liquid to a solid.

Evaporation (boiling)

Changing from a liquid to a gas.

Condensation

Changing from a gas to a liquid.

Sublimation

Changing straight from a solid to a gas, skipping the liquid stage.

Deposition

Changing straight from a gas to a solid.

Element

A pure substance made of only one kind of atom. Its number of protons tells which element it is.

Atom

The smallest unit of an element. It's made of protons, neutrons, and electrons.

Nucleus (of an atom)

The center of an atom. It holds the protons and neutrons.

Proton

A positive (+) particle in the nucleus of an atom.

Neutron

A particle with no charge, found in the nucleus.

Electron

A negative (−) particle found outside the nucleus.

Atomic number

The number of protons in an atom. It identifies the element.

Isotope

Atoms of the same element with different numbers of neutrons.

Mass number

The number of protons plus neutrons in an atom.

Compound

Two or more elements chemically joined. It has new properties of its own.

Molecule

Two or more atoms bonded together.

Chemical reaction

Bonds break and new bonds form, making new substances. Atoms are rearranged, never created or destroyed.

Reactant

A substance at the START of a chemical reaction. It's written on the left side of the arrow.

Product

A substance MADE by a chemical reaction. It's written on the right side of the arrow.

Solution

A mixture where one substance is completely dissolved in another.

Solute

The substance that gets dissolved.

Solvent

The substance that does the dissolving.

Homogeneous mixture

A mixture that looks the same all the way through.

Heterogeneous mixture

A mixture whose parts aren't evenly mixed. You can see the different parts.

Concentration

How much solute is in a certain amount of solution.

pH

A 0–14 scale that shows how acidic or basic a solution is. 7 is neutral.

Acid

A solution with a pH below 7. Lower pH means more acidic.

Base (alkaline)

A solution with a pH above 7. Higher pH means more basic.

Buffer

A solution that resists changes in pH.

Titration

A lab method that slowly adds a solution of known concentration to find the concentration of an unknown acid or base.

Indicator

A chemical that changes color at a certain pH.

Evolution

Change in a species over many generations.

Natural selection

Living things with helpful traits survive and reproduce more, so those traits become more common over time.

Trait

A characteristic of a living thing.

Gene

A section of DNA that carries instructions for a trait. The basic unit of heredity.

Speciation

When a new species forms during evolution.

Genotype

The genes an organism has.

Phenotype

The traits you can actually see or measure.

Allele

One version of a gene. You usually get one from each parent.

Dominant allele

An allele that shows its trait even when only one copy is present.

Recessive allele

An allele that shows its trait only when there are two copies.

Taxonomy

The science of classifying and naming living things: kingdom, phylum, class, order, family, genus, species.

Scientific name

A two-part name: genus first, then species. Written in italics, with only the genus capitalized.

DNA

The molecule that carries genetic instructions. Shaped like a twisted ladder (double helix) with bases A, T, C, and G.

RNA

A molecule that carries DNA's instructions so the cell can make proteins.

Codon

Three bases in a row that code for one amino acid.

Mutation

A change in the DNA sequence. It can be passed on to offspring.

Transcription

Copying DNA into mRNA. It happens in the nucleus.

Translation

A ribosome reads mRNA and builds a protein.

Amino acid

The building blocks of proteins.

Cell

The smallest unit of life.

Prokaryotic cell

A simple cell with no nucleus.

Eukaryotic cell

A larger, more complex cell with a nucleus and organelles.

Organelle

A structure inside a cell that has a specific job.

Nucleus (of a cell)

The part of a cell that holds its DNA.

Cell membrane

The barrier around a cell. It lets some things in and keeps others out.

Cell wall

A stiff outer layer around some cells, like plant cells.

Mitochondria

Organelles that turn food energy into energy the cell can use.

Ribosome

The organelle where proteins are made.

Carbohydrate

Sugars and starches. A main source of energy.

Lipid

Fats and oils. They don't dissolve in water and make up cell membranes.

Protein

A large molecule made of amino acids that does many jobs in living things.

Nucleic acid

DNA and RNA. They store and use genetic information.

Photosynthesis

How plants use light, water, and carbon dioxide to make sugar and oxygen.

Density

How much mass is packed into a space: mass ÷ volume.

Gravity

A force that pulls objects toward each other. It gives objects weight.

Speed

How far something travels in a certain amount of time.

Velocity

Speed in a certain direction.

Inertia

An object's resistance to changes in its motion. More mass means more inertia.

Momentum

Mass in motion: mass × velocity.

Kinetic energy

The energy of motion. Faster means more kinetic energy.

Potential energy

Stored energy because of an object's position.

Lens

A clear, curved object that bends light.

Refraction

The bending of light as it passes from one material into another.

Electromagnetic spectrum

The full range of light waves, from radio waves to gamma rays. Visible light is a small part.

Wavelength

The distance from one wave peak to the next.

Frequency

How many waves pass a point each second, measured in hertz (Hz). Longer wavelength means lower frequency.

Mineral

A natural, nonliving solid with a set chemical makeup and a crystal structure.

Rock

A natural solid mixture of one or more minerals.

Igneous rock

Rock formed when melted rock (magma or lava) cools and hardens.

Sedimentary rock

Rock formed from layers of bits of other rocks or once-living things. May contain fossils.

Metamorphic rock

Rock changed by high heat and pressure.

Fossil

The preserved remains or traces of a once-living thing.

Rock cycle

The slow, continuous process that changes rocks from one type to another.

Weathering

Breaking down rock at Earth's surface by natural forces.

Erosion

Moving broken-down rock and soil from one place to another.

Crust, mantle, core

Earth's layers from outside in: a thin rocky crust, a thick slowly flowing mantle, and an iron-nickel core.

Plate tectonics

The idea that Earth's outer layer is broken into large plates that move.

Seismic waves

Vibrations that travel through Earth, often caused by earthquakes.

Troposphere

The lowest layer of the atmosphere, where we live and most weather happens. It gets colder as you go up.

Stratosphere

The layer above the troposphere. It holds the ozone layer and gets warmer as you go up.

Ozone layer

Part of the stratosphere that absorbs most of the sun's UV light.

Greenhouse gas

A gas that lets sunlight in but traps heat, warming the atmosphere.

Air pressure

The weight of the air pressing down. It drops as you go higher.

Barometer

A tool that measures air pressure.